Various techniques for detecting an abnormality of a rotating machine (e.g., compressor, motor, generator) have been proposed. For example, a compressor diagnostic method for detecting an AE wave generated by contact between a male rotor and a female rotor during rotation of a rotor of a non-contact type compressor and a rotation signal of the rotor at that time, and for diagnosing rotor contact based on the detected AE signal and rotation signal has been proposed. The compressor diagnostic method includes amplifying and detecting the AE signal, performing a frequency analysis and an averaging process on the output, and comparing the result with determination criteria based on the rotation signal to diagnose the presence of rotor contact (e.g., refer to Patent Literature 1).
In addition, an abnormal contact detection method for detecting an abnormal contact state of a rotating machine in which a first rotor and a second rotor rotate in a pair has been proposed. The abnormal contact detection method includes: detecting an elastic wave signal emitted from the rotating machine; identifying contact between the rotors when the detected elastic wave signal includes a predetermined level or more of at least one of a rotational frequency component of the first rotor and a rotational frequency component of the second rotor; identifying contact between the rotor and a casing when the detected signal includes a predetermined level or more of a frequency component obtained by multiplying the number of blades of the first rotor by a rotation frequency of the rotor and a frequency component obtained by multiplying the number of blades of the second rotor by the rotation frequency of the rotor; and identifying contact between a sealant and the rotor when a waveform level of the elastic wave signal emitted from the rotating machine is larger than a predetermined level but the contact between the rotors and the contact between the rotor and the casing are not identified (e.g., refer to Patent Literature 2).
A main cause of a rotating machine abnormality is contact between rotating bodies or contact between a rotating body and a casing. While the rotating machine is in operation, an elastic wave is continuously generated from the rotating machine. When the contact occurs, a relatively large elastic wave occurs instantaneously. Using this principle, a rotating machine abnormality is detected. The elastic wave is detected using a vibration sensor or an ultrasonic sensor. Such a sensor uses a piezoelectric element, and when a temperature rises at a place where the sensor is disposed, sensitivity of the sensor decreases. Therefore, it is necessary to perform temperature compensation for the temperature rise.